Slow light to capture a rainbow

U. BUFFALO (US) — Scientists have taken a step toward a breakthrough in optical communications by slowing broadband light waves using a type of material called nanoplasmonic structures.

The ultimate goal, researchers say, is multiplexed, multiwavelength communications, where optical data can be tamed at different wavelengths, greatly increasing processing and transmission capacity.

If light could ever be stopped entirely, says Qiaoqiang Gan, assistant professor of electrical engineering at Univeristy at Buffalo, new possibilities would open up for data storage.

“At the moment, processing data with optical signals is limited by how quickly the signal can be interpreted,” he says. “If the signal can be slowed, more information could be processed without overloading the system.”

Gan and colleagues created the structures by making nanoscale grooves in metallic surfaces at different depths, which alters the materials’ optical properties.

The plasmonic chips provide the critical connection between nanoelectronics and photonics, Gan says, allowing different types of devices to be integrated, a prerequisite for realizing the potential of optical computing, “lab-on-a-chip” biosensors, and more efficient, thin-film photovoltaic materials.

The optical properties of the structures allow different wavelengths of light to be trapped at different positions, potentially allowing for optical data storage and enhanced nonlinear optics.

Light is slowed down so much that researchers are able to trap multiple wavelengths of light on a single chip, compared to conventional methods can only trap a single wavelength in a narrow band.

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“Light is usually very fast, but the structures I created can slow broadband light significantly,” says Gan. “It’s as though I can hold the light in my hand.”

Because the nanoplasmonic structures can trap very slow resonances of light, they can do so at room temperature, instead of at the ultracold temperatures that are required in conventional slow-light technologies.

“In the PNAS paper, we showed that we trapped red to green,” explains Gan. “Now we are working on trapping a broader wavelength, from red to blue. We want to trap the entire rainbow.

“This ultrafast light source will allow us to measure experimentally just how slow is the light that we have trapped in our nanoplasmonic structures,” Gan explains.

“Once we know that, we will be able to demonstrate our capability to manipulate light through experiments and optimize the structure to slow the light further.”